The present invention relates to borehole clean up, particularly a tool for cleaning up the stepped region of a wellhead.
Boreholes are typically lined with a concrete casing. In order to maximise production from the well it is necessary to clean out the casing, removing debris and contaminants.
One region of the borehole which is particularly hard to clean is the wellhead. The wellhead is stepped in diameter, with a larger diameter at the top. A typical profile is shown in FIG. 1. The diameters A, B, C and D are of commonly standardised dimensions, but there is some variation between steps E and F from well to well.
Due to the stepped profile, tools adapted to clean the main body of the borehole with brushes and jets of cleaning fluid will not be of the correct diameter to clean the upper steps. At the present time, the stepped profile of the wellhead cannot be properly cleaned.
Successfully cleaning the stepped region of the wellhead would significantly improve fluid flow in the region of the wellhead and so have benefits for production.
The primary aim of the present invention is to provide apparatus for cleaning stepped profile borehole casing.
A further aim of the present invention is to provide apparatus for cleaning stepped profile borehole casing that can adapt readily to the particular vertical distances between steps.
Running a workstring is time consuming and therefore expensive. For this reason, it is desirable to be able to run a workstring with tools to carry out a variety of functions. Therefore, a still further aim of the present invention is to provide apparatus for cleaning stepped profile borehole casing that can be integrated into a workstring and can also be employed only when required.
According to the present invention there is provided a cleanup tool for cleaning stepped regions of boreholes, the tool comprising a tool body into which fluid may flow axially, a plurality of radial outlets which correspond in position to the profile of a stepped region of a borehole and an engagable means for encouraging fluid to exit through the radial outlets.
Preferably, the tool body is adapted to be incorporated into a workstring.
The tool body may comprise a plurality of axially slidably mounted barrels adapted to rest on steps in the profile of a borehole and thereby to enable the position of the plurality of outlets to correspond to the profile of the stepped region of a borehole.
Springs may be provided to oppose the axial motion of the slidably mounted barrels.
The engagable means for encouraging fluid to exit through the radial outlets may comprise a valve activated by a ball dropped down the workstring.
Alternatively, the engagable means for encouraging fluid to exit through the radial outlets may comprise a valve that is engaged by the axial movement of a shear sleeve when the shear sleeve bottoms out on a step in a borehole.
Alternatively, the engagable means for encouraging fluid to exit through the radial outlets may comprise an outlet from which axially flowing fluid passes, a plug which acts to reduce fluid flow between the external surface of the tool and the internal surface of the borehole, and an inlet through which fluid may enter the body of the tool and subsequently exit through the radial outlets.
Preferably, the plug comprises a means for engaging a step in the internal surface of a borehole.
Preferably also, the means for engaging a step in the internal surface of a borehole comprises a curved profile.
Preferably also, the means for engaging a step in the internal surface of a borehole may be rotatably mounted on the tool body.